MetLife Inc., the largest U.S. life insurer, raised $3.15 billion by selling shares below Monday's closing price to help pay for the acquisition of an American International Group Inc. business unit.

MetLife said it sold 75 million shares at $42 each, compared with Monday's closing price of $42.73. MetLife, based in New York, closed at $38.92 on March 5, the last day of trading before the announcement of the $15.5 billion deal to purchase AIG's American Life Insurance Co.

The insurer initially planned to sell $2 billion of shares to help finance the acquisition.

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